This invention relates to reflector-type lamps and, more particularly, to reflector-type high-intensity-discharge lamps which incorporate a particular dichroic coating.
Incandescent lamps utilizing a reflector incorporated as a coating on the interior surface of the lamp envelope is well known. The reflective coating is typically composed of aluminum.
Dichroic reflective coatings may be used when it is desirable to reflect infrared radiation and transmit visible light or vice versa. One application using a dichroic reflector of the former type in a high-pressure sodium vapor lamp is disclosed in U.S. Pat. No. 3,931,536, issued to Timothy Fohl et at., dated Jan. 6, 1976. The Fohl patent discloses the use of a reflective filter carried as a coating on the lamp envelope that selectively reflects arc discharge radiation in the infrared region of the electromagnetic spectrum to which the arc tube walls are transparent and to which the arc plasma is optically thick, so that the reflected infrared radiation is preferentially absorbed by the arc plasma to improve lamp efficiency. A second application utilizing the latter type of dichroic reflector i.e., one that reflects visible light and transmits infrared radiation, is in conjunction with incandescent lamps having special applications, such as illuminating frozen food and produce showcases where the introduction of heat is undesirable or for use in store windows to reduce fading of merchandise.